1. Field of the Invention
This invention relates to junction devices and, more particularly, to metal oxide junction devices.
2. Art Background
Flat large area display devices are a desirable goal for many applications, such as large area television screens. As a first step in achieving this goal, it is necessary to produce a thin film device which can function as an element of a large array. To be suitable for most commercial applications these device elements should have certain general properties. First, because many elements are necessary to form an array, they should be relatively inexpensive. Further, these devices should operate on voltages typically used with integrated circuitry and should have a long lifetime at room temperature.
Various flat luminescent display devices have been demonstrated, but none, as yet, entirely satisfy these criteria. For example, plasma or electroluminescent panels have been made. The former type panels consist of a small quantity of gas encapsulated between transparent plates. A discharge is initiated in the gas which then emits visible light. Such panels require a high voltage, typically 150 volts, to produce the discharge. The latter type panels operate by applying an a.c. or d.c. voltage to a layer of semiconductor material such as ZnS. Again, a high voltage (typically several hundred volts) is necessary to produce light emission. Therefore, these devices are not usable in conjunction with integrated circuitry.
A second type display device, which is presently widely used, is light emitting diodes. These diodes utilize low voltages, typically 2 volts, and are stable at room temperature. However, the semiconductor materials usually used in these diodes and the cost of the processing necessary to form the diodes from the semiconductor materials makes them relatively expensive devices. Although this expense is not significant for uses that require a small number of characters such as in digital watches, applications which require a large array of such devices are often economically precluded.
Another recently reported display device (See McCarthy and Lambe, Appl. Phys. Lett., 30, 427 (1977)) is a tunnel junction composed of an aluminum oxide layer between an aluminum and silver electrode. This device operates at low voltages, e.g., 2 to 5 volts as do light emitting diodes. Unlike light emitting diodes, this device utilizes inexpensive materials and is formed by relatively economical processing steps. Unfortunately, for typically applied voltages this device based on an aluminum oxide barrier is only stable at low temperatures, e.g., liquid nitrogen temperatures. Attempts to operate this device at room temperature produce an instantaneous destruction of the device. For these reasons, none of these currently available devices possess all the previously enumerated attributes.